Successful send as a trigger.

In a script, I am drawing a recordset that determines if the client has already been sent an invoice. If it has not, (recordset empty trigger), the email is sent. On a successful email send, I want to update the database record to reflect that the email invoice was sent, but an unset session variable could also mean the email just was never sent because it did not need to be sent.

I thought this was typically a trigger (any successful email send), but it is not appearing in my list of values .

What value can I read that will trigger an update transaction if an email is successfully sent, but not if there is an error OR if not email is sent at all.